In recent years, standardization of ITU-T Y.1731 OAM (Operations Administration and Maintenance), IEEE 802.3ag as an OAM function of Ethernet (Registered Trademark) is progressing and the demand for a communication apparatus having an OAM function for accommodating Ethernet lines is growing. In the following description, WAN (Wide Area Network) and MAN (Metropolitan Area Network) are included in the term “LAN (Local Area Network)”. Further, Ethernet (Registered Trademark) signals may also be referred to as LAN signals; Ethernet (Registered Trademark) frames may also be referred to as LAN frames; Ethernet (Registered Trademark) lines may also be referred to as LAN lines; and Ethernet (Registered Trademark) network may also be referred to as LANs.
The term “OAM”, an abbreviation for Operations, Administration, and Maintenance and represents a maintenance function. In this case, in using Ethernet (Registered Trademark) OAM, an OAM dedicated message (hereinafter also simply referred to as “OAM message”) is included in a LAN frame. This LAN frame is referred to as an “E-OAM frame” or an “OAM frame”. By transmitting/receiving the E-OAM frame on a LAN frame communications network, communications status (e.g., disconnection) between communication apparatuses can be monitored.
In a communication apparatus accommodating a LAN line(s), the communication apparatus is typically adaptable to a VLAN (Virtual LAN). Further, the OAM function is desired to be applicable with respect to each VLAN (i.e. in VLAN units). Typically, in a LAN provided by a carrier, each user is managed with a different VLAN. Accordingly, by providing the OAM function in VLAN units, the carrier can perform monitoring/maintenance on the LAN line with respect to each user managed in VLAN units. Thus, maintenance can be provided with higher reliability.
The OAM function includes various messages such as CC (Continuity Check), LB (Loop Back), and LT (Link Trace). The communication apparatus including the OAM function is to include different OAM messages in VLAN units.
Each OAM frame can be set with a desired OAM level. With the OAM frame, different OAM levels can be set for each communication apparatus in the same VLAN. Accordingly, different sections in the LAN can be monitored.
FIG. 1 is a schematic diagram of a communication apparatus according to a related art example. In FIG. 1, function parts of the transmitting side are not illustrated. In FIG. 1, interface cards 10 transmit/receive LAN frames. A switch card (SW card) 20 performs exchanging of LAN frames between the interface cards 10. A CPU (Central Processing Unit) card 30 is for performing setting/monitoring on each of the cards 10, 20. The CPU card 30 is connected to each card 10, 20 for transmitting/receiving control signals. By using the control signals, the CPU card 30 can set table information or gather, for example, failure alarm information.
A PHY+MAC part 11 provided in the interface card 10 has a PHY portion and a MAC portion. The PHY portion performs predetermined processes for LAN frame transfer in the physical layer. The MAC portion performs predetermined processes for LAN frame transfer in the MAC layer. An access control part 12 controls transmission of search data to a frame determination table part 13 and receiving read out data from the frame determination table part 13.
The frame determination table part 13 includes a frame determination table. The frame determination table part 13 receives search data from the access control part 12 and searches the frame determination table for matching registered search data. In a case where matching registered search data (Hit:Match) are found, the frame determination table part 13 transmits data (read out data) read out from an entry corresponding to the matching registered search data. The read out data include information indicating results of determining whether a frame is an OAM frame. In a case where no matching registered search data are found (No Hit:No Match), the frame determination table part 13 transmits data indicating that there are no data matching the frame (no hit). For example, CAM (Content Addressable Memory) may be used as the frame determination table part 13.
A selecting part 14 selects a subsequent process of a corresponding frame based on determination results (e.g., whether the frame is an OAM frame, whether no matching registered search data are found) received from the access control part 12. In a case where a frame is determined to be an OAM frame by the frame determination table part 13, the selecting part 14 transfers the frame to an OAM terminating part 15. The OAM terminating part 15 performs an OAM terminating process on a frame determined to be an OAM frame by the frame determination table part 13. In a case where a frame is determined as not being an OAM frame (non-OAM frame) by the frame determination table part 13, the selecting part 14 transfers the frame to the Switch card 20. In a case where a frame is determined as no hit by the frame determination table part 13, the frame is discarded.
FIG. 2A illustrates a VLAN frame format, and FIG. 2B illustrates an E-OAM frame format attached with a VLAN frame. In FIGS. 2A and 2B, the numerals in the parentheses indicate the number of bits. Further, “MAC DA” indicates a MAC destination address, and “MAC SA” indicates a MAC origin address. Further, “Ether Type” indicates a frame type of a corresponding frame. For example, the value indicated in Ether type differs depending on whether the frame is, for example, a VLAN frame, an IP frame, or an OAM frame. In this example, the Ether Type corresponding to a VLAN frame is “0×8100”, the Ether Type corresponding to an IP frame is “0×800”, and the Ether Type corresponding to an OAM frame “0×9900”.
Further, “FCS (Frame Check Sequence)” indicates Cyclic Redundancy Code (CRC)-32 data installed at a rearmost of a frame. FIG. 2A illustrates a case where an IP frame is installed in a VLAN frame. FIG. 2B illustrates a case where an OAM frame is installed in a VLAN frame.
As illustrated in FIG. 2B, the OAM frame includes various data such as MEL, V, and OPC. In FIG. 2B, “MEL” indicates OAM level data, “V” indicates version data, and “OPC” indicates Operation Code data. “Others” include data that differ according to each type of OAM message.
FIG. 3 illustrates an exemplary configuration of entries of a frame determination table of the frame determination table part 13. In FIG. 3, the numerals in the parentheses indicate the number of bits. The frame determination table part 13 is configured as a CAM (Content Addressable Memory). The CAM includes search data and readout data corresponding to the search data.
In this example, data are extracted from a predetermined area of an input LAN frame and transmitted as search data to the CAM. Then, it is determined whether there are data matching the search data. According to the determination result, the type of frame is determined.
In FIG. 3, the following entries are stored in the CAM. Entries 1-3 are each an entry of a VLAN+OAM frame. In order to provide the OAM function in VLAN units, data containing a VLAN tag are registered as search data in the frame determination table. In FIG. 3, the part corresponding to “Mask” (which indicates “don't care”) is not a search target.
Further, in FIG. 3, “A” (which indicates “Availability”) is referred for determining whether an entry of the CAM is valid or invalid. For example, “A=1” that an entry is valid. Further, “MEL”, “V”, and “OPC” are registered as search data for determining the level, version, and type of OAM, respectively. “OPC” indicates various types of OAM messages. For example, “0×01” (“0×0” is a prefix for representing hexadecimal numerals) indicates a CC message, “0×02” indicates an LBR message, and “0×03” indicates an LBM message. An entry containing an OPC is added with respect to each type of OAM of each VLAN.
The “OAM” of the readout data indicates a non-OAM frame where OAM=0 and indicates an OAM frame where OAM=1. The “OAM Type” of the readout data indicate the type of OAM of each entry. For example, in a case where OAM=0, the content of “OAM Type” is invalid because the frame is a non-OAM frame. “Discard” indicates whether the frame is to be discarded. For example, in a case where the frame is to be discarded, “Discard=1”. Further, “output card number” and “output port number” are stored in the readout data.
Because an OAM frame ends at the interface card receiving the OAM frame, the output card number and the output port number in the readout data are invalid. In FIG. 3, Entry 4 is an entry of a VLAN+non-OAM frame. The frame matching this entry is determined as a non-OAM frame. After obtaining the output card number and the output port number from the readout data, the non-OAM frame is transferred to the switch card 20 and transmitted to a corresponding output port of an interface card 10 at the output side via the switch card 20.
Entry N is an entry of a no-hit frame. The entry N is stored in a rearmost part of the frame determination table 13. The searching operation in the CAM (Content Addressable Memory) is started from a high order (low number) address of the frame determination table. In a case where a match is found (hit), the frame determination table part 13 ends searching and transmits corresponding readout data matching the entry to the access control part 12.
In this example, low number addresses are located at the upper side of the frame determination table. Thus, in a case where search data match none of the entries, the search data finally match the rearmost entry (No-hit entry). Because the no-hit entry is entirely formed of a mask portion except for the “A (Availability)” portion, the no-hit entry will match the search data regardless of the content of the search data. In this case, the frame matching the no-hit entry is to be discarded as indicated in the “discard” portion (indicated as “1”) of the readout data. An ending operation of E-OAM is described below.
With reference to FIG. 1, in a case where a frame is input to the interface card 10, the PHY+MAC part 11 receives the frame. After predetermined processes in the physical layer and the MAC layer are performed on the frame, the access control part 12 extracts data starting from the top (header) to 160 bits, assigns a valid bit “A” (for the frame determination table part 13) to the top (header) of the extracted data, and transmits the extracted data as search data to the frame determination table part 13. The frame determination table part 13 searches its frame determination table based on the search data received from the access control part 12 and determines whether there are any matching registered search data. The result of the search is transmitted to the access control part 12.
Then, the selecting part 14 selects a subsequent process based on the search/determination result of the frame determination table part 13.
Accordingly, the type of received frame is determined and an appropriate process is performed on the frame based on the determination result.
It is to be noted that, there is proposed a configuration of a L2 switch having a VLAN function in which a VLAN function part maps a frame to a predetermined VLAN, a frame categorizing part prioritizes the frame, and an OAM monitoring part inserts a monitoring frame in the VLAN (see, for example, International Publication Pamphlet No. WO2004/040854).
According to a related art example, in a case of setting OAM to each VLAN, it is necessary to set single VLAN+non-OAM frame entries and plural VLAN+OAM frame entries
A typical communication apparatus is required to accommodate several thousands of VLANs. Further, another communication apparatus is to accommodate several ten thousands of VLANs in a case of double-tagging (e.g., Q-in-Q).
In a case of setting plural OAM messages in VLAN units, the number of necessary table entries increases significantly. However, due to the limited capacity of CAM, a necessary number of VLANs and OAM functions cannot be set.
In order to set an OAM function(s) with respect to a required number of VLANs, memory capacity of a frame determination table needs to be increased significantly and the number of components is to be increased. This leads to an increase of manufacturing cost and an increase of power consumption.